Energy v cost, do people really not know the difference?

[ericmark]

I remember a lecture by Sir Richard Davies in Leiston Suffolk on the early days of radar, and he explained when they found dead seagulls around the Orford Nest test site, how they were sent away for analyst, It seems they were landing ready cooked, so they tried to make a death ray, this did not work, but the research is what resulted in the microwave cooker.

I would have thought the frequency will matter, and it may well be some microwaves use slightly different frequencies, so better suited for some types of food.

But be it boiled in a kettle, or in a microwave, shaking water at boiling point can cause it to reboil, I had a nasty scald, from a stainless steel pump action flask, when I picked it up and the water reboiled, forcing it out of the spout. Never picked one up by the body again, always use the handle.

 

[Harry Bloomfield]

Interesting. As a matter of interest, how do you know that? I couldn't tell you what sort of counter/clock any of my appliances have.

Accuracy, while ever the mains supply continues, the mains supply is allowed to lose, or gain a little, but will always be accurate within a few seconds per day - there is no long term drift. Synched by radio, is highly unlikely, they would point this out, as a feature in the handbook. Yes, they could be quartz, but all quartz systems exhibit some drift over an extended period.

 

[JohnW2]

I remember a lecture by Sir Richard Davies in Leiston Suffolk on the early days of radar, and he explained when they found dead seagulls around the Orford Nest test site, how they were sent away for analyst, It seems they were landing ready cooked, so they tried to make a death ray, this did not work, but the research is what resulted in the microwave cooker.

It was certainly the development of radar which facilitated the appearance of microwave cookers as we know them, since it resulted in the development of cavity magnetrons. They probably were not trying (but who knows?!) to develop a 'death ray', but some the early radar research probably used some high energy radiation which were capable of 'doing harm'!

I would have thought the frequency will matter, and it may well be some microwaves use slightly different frequencies, so better suited for some types of food.

Frequency certainly matters, and heating of things with electromagnetic radiation is not restricted to microwaves. I think you'll find that some of the early work used fairly low ('HF') 'radio frequencies, maybe as low as 10 or 20 MHz in some cases.

I think that surgical diathermy still uses 'HF' (i.e. 'sub-VHF').

 

[JohnW2]

Accuracy, while ever the mains supply continues, the mains supply is allowed to lose, or gain a little, but will always be accurate within a few seconds per day - there is no long term drift.

Indeed. I seem to recall that there are very tight limits on the amount of allowed variation of total number of cycles in a 24 hour period.

Synched by radio, is highly unlikely, they would point this out, as a feature in the handbook.

They would - but that would be ridiculously OTT for a cooker or other domestic appliance

Yes, they could be quartz, but all quartz systems exhibit some drift over an extended period.

I must say that I never cease to be amazed at how little long-term drift one sees in (often ludicrously cheap) quartz clock etc. movements (I recently bought some for wellunder£1 each!). I suppose a lot of the 'drift' will be due to temperature changes and, over an extended period, they may well tend to cancel out.

So, your belief that your appliances have mains-synchronised clocks is a guess based on their being accurate? (and I assume that you never 'switch off' your appliances or have power cuts?)

 

[Harry Bloomfield]

So, your belief that your appliances have mains-synchronised clocks is a guess based on their being accurate? (and I assume that you never 'switch off' your appliances or have power cuts?)

Normally, we do not switch them off, it's too much of faff, to work out how to reset the clocks. Our last power cut, maybe a decade ago.

 

[JohnW2]

Normally, we do not switch them off, it's too much of faff, to work out how to reset the clocks.

That is, of course, the discussion we've been having

Although you talked about lack of drift over 'extended periods of time' (and based your assumption of mains-synchronisation on that), and say that it's a decade since you've had a power cut, you presumably have to reset the clocks every 6 months (like a couple of days ago) - unless, of course, you leave your clocks on GMT all the time!

 

[Harry Bloomfield]

Although you talked about lack of drift over 'extended periods of time' (and based your assumption of mains-synchronisation on that), and say that it's a decade since you've had a power cut, you presumably have to reset the clocks every 6 months (like a couple of days ago) - unless, of course, you leave your clocks on GMT all the time!

You don't need to do a full reset, just to + or - 1 hour, why would you?

 

[JohnW2]

You don't need to do a full reset, just to + or - 1 hour, why would you?

Ah - cunning these Chinese

 

[morqthana]

I've not used my car since Saturday. Looking forward to the sight of the analogue clock in in it running forward by 11 hours when I next turn on the ignition.

 

[endecotp]

I would suggest most appliance clocks are mains synchronised. Why would they not be?

I reckon appliances will use whatever is cheapest to make, most of the time, and my guess is that a mains-synchronised digital clock will cost more than one with a 32 kHz quartz crystal.

I say that because the 50 Hz input to the clock logic probably needs to be safety-isolated from the mains, which means an opto-isolator or a transformer. When there was a transformer anyway to get the DC for the digital clock logic, that wasn’t a problem - but with a modern switched-mode supply, it needs extra components.

Who’s going to take their oven apart to see how it actually works?

 

[Harry Bloomfield]

Who’s going to take their oven apart to see how it actually works?

I pulled apart my last, failed, microwave oven. That was certainly mains synched, no sign of a crystal. However, a further point occurs, in that if a 32kHz oscillator were used, that would be ridiculously easy to keep going through a power cut, with a battery, or even a cap. They don't, simply because they are mains synched, so we end up resetting them at every power loss.

I say that because the 50 Hz input to the clock logic probably needs to be safety-isolated from the mains, which means an opto-isolator or a transformer.

A transformer will certainly be involved anyway, for the supply to the electronics - why not tap into it, for the 50Hz signal?

 

[JohnW2]

A transformer will certainly be involved anyway, for the supply to the electronics - why not tap into it, for the 50Hz signal?

The transformer in a SMPSU surely not only operates at a frequency much higher than 50Hz but at a frequency which is essentianly 'arbitrary' - so useless for synchronising anything?

 

[endecotp]

A transformer will certainly be involved anyway, for the supply to the electronics

Almost nothing has a 50 Hz transformer any more, it’s all switched-mode.

I’m unsure about how the supply to the magnetron in a modern microwave works though.

 

[Harry Bloomfield]

The transformer in a SMPSU surely not only operates at a frequency much higher than 50Hz but at a frequency which is essentianly 'arbitrary' - so useless for synchronising anything?

Are you really suggesting, that you could find no easy way to source 50Hz from the mains, despite SMPSU's?

 

[Harry Bloomfield]

I’m unsure about how the supply to the magnetron in a modern microwave works though.

Most, work using a large, very heavy, mains, to high voltage transformer, followed by a rectifier.